Various analytical techniques for highly sensitive liquid chromatography/mass spectrometry (LC/MS) and their applications in forensic chemistry have been investigated. The following three types of LC/MS instruments were used for this study: 1) a Micromass model PLATFORM II equipped with an atmospheric pressure chemical ionization (APCI) or an electrospray ionization (ESI) interface; 2) a Shimadzu model QP-1100EX combined with a thermospray TSP interface; 3) a JEOL model JMS-SX102A fitted with a Frit - fast atom bombardment ionization (Frit-FAB) interface. Optimization of capillary voltage and the flow rate of the mobile phase were found for ESI-LC/MS. The relationship between the composition of mobile phase and ionization efficiency was investigated in the ESI, APCI and TSP types of LC/MS. In ESI-LC/MS analysis, the use of a semi-micro column (1.5 mm I.D.) allowed about ten rimes more sensitive an analysis than a conventional column (4.6 mm I.D.). In order to examine the provable period of triazolam, which is quickly metabolized, urine samples obtained from four volunteers who had taken 0.25 or 0.5 mg of the drug were analyzed by TSP-LC,IRIS. The main urinary metabolite of triazolam, alpha-hydroxytriazolam (alpha-HT) was detectable up to 36 hours after taking the dosage. For the purpose of checking the detectable period of suxamethonium in post-mortem biological samples, Frit-FAB LC/MS analysis was performed for the tissue samples of the rats which died by the intraperitoneal administration of the drug at 10 mg/kg bodyweight. Suxamethonium in the rat liver was detectable up to 42 days later, as long as the bodies were stood at 0 degrees C immediately after the death.